Many types of optical microelectromechanical systems (“MEMS”) have surfaces coated with reflective coatings (e.g., gold with underlayers). For example, one such type of MEMS devices is an optical switch used in telecommunications systems. In this application, a coated surface performs the function of a mirror to reflect light beams in a specified manner. To reflect light beams in the manner specified, a reflective coating must be precisely deposited onto its underlying wafer. Undesirably, it is difficult to precisely deposit coatings onto MEMS structures.
One commonly used coating deposition method, known in the art as “shadow mask deposition,” applies coatings through apertures in a thin film (i.e., the film being known in the art as a “shadow mask” or “mask”). To these ends, currently available masks typically consist of a thin metal foil with a plurality of etched apertures. Such masks, however, have a number of problems. Specifically, since metal masks commonly are both flexible and not flat, it is difficult to precisely align them to a wafer. In some instances, imprecise mask/wafer alignment can cause the film to be deposited onto the wrong area of the wafer. Moreover, the coefficient of thermal expansion of metals typically used for metal shadow masks is different than that of silicon (i.e., the material of the underlying wafer). Accordingly, as the coating is deposited, the respective temperatures of the mask and wafer increase, further misaligning the mask and wafer. In some instances, the thermal expansion and contraction of the mask can alter the intended shape of the apertures, consequently distorting the intended shape of the coating on the MEMS device.